Light guide, light source apparatus and endoscope system

Abstract

A large diameter fiber is composed of a multimode optical fiber and provided with a fiber body having a constant diameter in an optical axis direction XA and a tapered section tapered in diameter toward a light exit surface. An adhesive member attaches the large diameter fiber inside a retaining hole of a tubular housing such that an outer circumferential surface of a tapered clad of the tapered section is entirely exposed to air to a predetermined depth from the light exit surface. A light passing space is a ring-like space formed between the exposed outer circumferential surface of the tapered clad and an inner circumferential surface of the tubular housing. Light in the tapered section is output from the light exit surface and partially leaked to the tapered clad. A part of the leaked light is released from the light passing space.

What is claimed is: 
     
       1. A light guide for transmitting light and outputting said light from a light exit surface comprising:
 a tubular housing; 
 a multimode optical fiber inserted through said housing, said multimode optical fiber having a core and a clad covering an outer circumferential surface of said core, said core having a tapered core whose diameter decreases toward said light exit surface, said clad having a tapered clad whose outer circumferential surface is inclined to be tapered along an outer circumferential surface of said tapered core toward said light exit surface, and 
 a transparent adhesive member provided between said housing and an outer circumferential surface of said clad, said adhesive member retaining said multimode optical fiber in said housing, said adhesive member having a lower refractive index than said clad, said adhesive member having a light passing space hollowed out to a predetermined depth from said light exit surface so as to expose at least a part of said outer circumferential surface of said tapered clad to air. 
 
     
     
       2. The light guide of  claim 1 , wherein said light passing space is a ring-like space formed between an inner surface of said housing and said outer circumferential surface of said tapered clad entirely exposed to said air to said predetermined depth. 
     
     
       3. The light guide of  claim 1 , wherein said light passing space is composed of a first space and a second space, and each of said first and second spaces has a tubular shape and is formed between said partly exposed outer circumferential surface of said tapered clad and an inner surface of said housing, and said first space is provided in a location opposite to said second space relative to said tapered core and said tapered clad. 
     
     
       4. The light guide of  claim 3 , wherein a radiation pattern of said light from said light exit surface is elliptical in shape. 
     
     
       5. The light guide of  claim 1 , wherein a numerical aperture (NA) of said light from said light exit surface is at least 0.35. 
     
     
       6. A method of forming a light passing space of a light guide, comprising steps of:
 inserting a multimode optical fiber into a housing, said multimode optical fiber having a core and a clad covering an outer circumferential surface of said core, said core having a tapered core whose diameter decreases toward a light exit surface, said clad having a tapered clad whose outer circumferential surface is inclined to be tapered along an outer circumferential surface of said tapered core toward said light exit surface; 
 attaching said multimode optical fiber in said housing by providing said adhesive member containing a UV hardening adhesive and by hardening said adhesive member by UV irradiation, and said adhesive member is provided between said outer circumferential surface of said clad and an inner surface of said housing in a state that said light exit surface of said multimode optical fiber and an end surface of said housing are made level with each other; and 
 removing said adhesive member by irradiating laser in a UV wavelength range to be absorbed by said adhesive member onto said adhesive member such that at least a part of said outer circumferential surface of said tapered clad is exposed to said air to said predetermined depth from said light exit surface. 
 
     
     
       7. A light source apparatus comprising:
 a light source; 
 a tubular housing; 
 a multimode optical fiber for transmitting light from said light source and inserted through said housing, said multimode optical fiber having a core and a clad covering an outer circumferential surface of said core, said core having a tapered core whose diameter decreases toward a light exit surface, said clad having a tapered clad whose outer circumferential surface is inclined to be tapered along an outer circumferential surface of said tapered core toward said light exit surface; and 
 a transparent adhesive member provided between said housing and an outer circumferential surface of said clad, said adhesive member retaining said multimode optical fiber in said housing, said adhesive member having a lower refractive index than said clad, said adhesive member having a light passing space hollowed out to a predetermined depth from said light exit surface so as to expose at least a part of said outer circumferential surface of said tapered clad to air. 
 
     
     
       8. An endoscope system comprising:
 A. a light source apparatus including:
 a light source; 
 a tubular housing; 
 a multimode optical fiber for transmitting light from said light source and inserted through said housing, said multimode optical fiber having a core and a clad covering an outer circumferential surface of said core, said core having a tapered core whose diameter decreases toward a light exit surface, said clad having a tapered clad whose outer circumferential surface is inclined to be tapered along an outer circumferential surface of said tapered core toward said light exit surface; and 
 a transparent adhesive member provided between said housing and an outer circumferential surface of said clad, said adhesive member retaining said multimode optical fiber in said housing, said adhesive member having a lower refractive index than said clad, said adhesive member having a light passing space hollowed out to a predetermined depth from said light exit surface so as to expose at least a part of said outer circumferential surface of said tapered clad to air; 
 
 B. an endoscope having an image sensor, said image sensor taking an image of a body cavity illuminated with said light from said light exit surface; and 
 C. an image processing apparatus connected to said endoscope, said processing apparatus processing a signal from said image sensor and forming an image.